手写 Promise.race

作者：安静

function isPromise(value) {
  if (
    typeof value === "function" ||
    (typeof value === "object" && value !== null)
  ) {
    if (typeof value.then === "function") {
      return true;
    }
  }
  return false;
}
Promise.myRace1 = (values) => {
  return new Promise((resolve, reject) => {
    for (let i = 0; i < values.length; i++) {
      const current = values[i];
      if (isPromise(current)) {
        current.then(resolve, reject); //一旦成功就直接停止
      } else {
        resolve(current);
      }
    }
  });
};

作者：
作者：gochri

/**
 * @param {Array/Map/Set[Promise]} promiseList
 * @return {Promise}
 */
const promiseRace = (promiseList = []) => {
    return new Promise((resolve, reject) => {
        // [] 时永远等待
        // if (promiseList.length === 0) { resolve() }
        for (let i in promiseList) {
            let promise = promiseList[i];
            Promise.resolve(promise)
                .then((res) => {
                    // return first resolve
                    resolve(res);
                })
                .catch((rej) => {
                    // return first reject
                    reject(rej);
                });
        }
    });
};
// ------- Test Case -------
let promise = Promise.resolve(1);
let promise1, promise2, promise3;
// Case 1
promise = promiseRace([]);
// promise
//     .then((values) => {
//         console.log("values", values);
//     })
//     .catch((error) => {
//         console.log("error", error);
//     });
// values undefined
// Case 5:default case
// promise1 = new Promise((resolve, reject) => {
//     setTimeout(resolve, 500, 'one');
// });
// promise2 = new Promise((resolve, reject) => {
//     setTimeout(resolve, 100, 'two');
// });
// promiseRace([promise1, promise2]).then((value) => {
//     console.log(value);
//     // Both resolve, but promise2 is faster
// });
// expected output: "two"
// Case 6: 异步性
// var resolvedPromisesArray = [Promise.resolve(33), Promise.resolve(44)];
// var p = promiseRace(resolvedPromisesArray);
// // immediately logging the value of p
// console.log(p);
// // using setTimeout we can execute code after the stack is empty
// setTimeout(function () {
//     console.log('the stack is now empty');
//     console.log(p);
// });
// Promise { <pending> }
// {/* the stack is now empty */ }
// {/* Promise { 33 } */ }
// Case7: setTimeout
var p1 = new Promise(function (resolve, reject) {
    setTimeout(resolve, 500, "one");
});
var p2 = new Promise(function (resolve, reject) {
    setTimeout(resolve, 100, "two");
});
promiseRace([p1, p2]).then(function (value) {
    console.log(value); // "two"
    // 两个都完成，但 p2 更快
});
var p3 = new Promise(function (resolve, reject) {
    setTimeout(resolve, 100, "three");
});
var p4 = new Promise(function (resolve, reject) {
    setTimeout(reject, 500, "four");
});
promiseRace([p3, p4]).then(function (value) {
    console.log(value); // "three"
    // p3 更快，所以它完成了
}, function (reason) {
    // 未被调用
});
var p5 = new Promise(function (resolve, reject) {
    setTimeout(resolve, 500, "five");
});
var p6 = new Promise(function (resolve, reject) {
    setTimeout(reject, 100, "six");
});
promiseRace([p5, p6]).then(function (value) {
    // 未被调用
}, function (reason) {
    console.log(reason); // "six"
    // p6 更快，所以它失败了
});
// two
// three
// six

作者：奥兰度

Promise.myRace = (promiseList) => {
  return new Promise((resolve, reject) => {
      promiseList.forEach(promise => {
        promise.then(val => {
          resolve(val)
        }).catch(err => {
          reject(err)
        })
      })
  })
}